The present invention relates generally to the preparation of heterocycles containing one or more nitrogen or oxygen heteroatoms, and in particular to the synthesis of such heterocycles utilizing a 1,3-dihalopropene such as 1,3-dichloropropene as a starting material.
As further background, heterocyclic compounds such as pyridines, pyrimidines, oxazoles, pyrazoles and quinolines enjoy a wide range of utilities including serving as actives and intermediates in the fields of herbicidal, pesticidal, and medicinal compounds. While many such compounds occur naturally and in the past have been isolated from natural sources, currently, most of the world""s supply of such compounds derives from synthetic preparations. Thus, a wide variety of syntheses are known in which one or more acyclic starting materials are reacted either to directly form the heterocycles or to form cyclizable intermediates which can then be converted to the heterocycles.
In light of this background the applicants have undertaken an investigation to discover new and useful routes to the above-mentioned heterocycles which employ readily-available starting materials and which can be conveniently conducted in standard laboratory or commercial equipment. In so doing the applicants have discovered that 1,3-dihalopropenes provide useful 3-carbon fragments for the production of such heterocycles including, for instance, 2,3-substituted pyridines, 2,5-substituted pyridines, pyrimidines, oxazoles, pyrazoles and quinolines.
Accordingly, in one broad aspect, the invention provides for the use of a 1,3-dihalopropene in the production of a heterocycle containing one or more nitrogen or oxygen heteroatoms, including for example pyridines, quinolines, pyrimidines, pyrazoles and oxazoles.
In broad aspects the invention thus provides a process for preparing a heterocycle having one or more nitrogen or oxygen heteroatoms, comprising reacting a 1,3-dihalopropene compound of the formula: 
wherein X is halo, R1 is H or R4 wherein R4 is H or a straight chain lower alkyl or benzyl group, and R2 and R3 are each H or a straight chain lower alkyl or benzyl group, with:
(1) acrylonitrile so as to form a cyclizable intermediate, and then cyclizing said intermediate to form a corresponding 2-halo-5-substituted pyridine compound, with the proviso that R1 is H;
(2) a compound of the formula CNxe2x80x94CH2xe2x80x94R5 wherein R5 is COOR6, CN, CON(R6)2, or COR6, wherein R6 is H or an alkyl, aryl or aralkyl group having 1 to about 10 carbon atoms, so as to form a cyclizable intermediate, and then cyclizing said intermediate to form a corresponding 2-halo-3-substituted-pyridine compound;
(3) a compound of the formula H2Nxe2x80x94NHR7 wherein R7 is H or an alkyl, aryl or aralkyl group having up to about 10 carbon atoms, so as to form a cyclizable intermediate; and then cyclizing said intermediate to form a corresponding pyrazole compound;
(4) hydroxylamine so as to form a cyclizable intermediate, and then cyclizing said intermediate to form a corresponding oxazole compound;
(5) a compound of the formula H2Nxe2x80x94CZxe2x80x94NH2 wherein Z is O, S or NH, so as to form a cyclizable intermediate, and then cyclizing said intermediate to form a corresponding pyrimidine;
(6) an aniline compound of the formula 
wherein R8, R9, R10 and R11 are each H or an alkyl, aryl or aralkyl group having up to about ten carbon atoms, so as to form a corresponding N-(3-halo-2-propenyl)aniline compound, and then cyclizing the an N-(3-halo-2-propenyl)aniline compound to form a corresponding quinoline compound; or
(7) a compound of the formula CNxe2x80x94XCxe2x88x92xe2x80x94R5 wherein X is halo, R5 is COOR6, CN, CON(R6)2, or COR6, wherein R6 is H or an alkyl, aryl or aralkyl group having 1 to about 10 carbon atoms, so as to form a cyclizable intermediate, and then cyclizing said intermediate to form a corresponding 2-halo-3-substituted-pyridine.
One specific, preferred embodiment of the invention provides a process for preparing a 2-halo-5-(methyl or halomethyl)-pyridine which includes the step of reacting a 1,3-dihalopropene with acrylonitrile to form a cyclizable intermediate compound, and cyclizing the intermediate compound to form the indicated 2,5-substituted pyridine. In one preferred mode of carrying out this process, the cyclization can be conducted in the presence of a halogenating agent, and the product is a 2-halo-5-halomethyl-pyridine. In another preferred mode, the cyclization is conducted in the absence of the halogenating agent, and the product is a 2-halo-5-methyl-pyridine. In addition, the 1,3-dihalopropene starting material can be substituted with additional groups to form further substituted pyridines. For example, provided by the present invention are processes for preparing a 2-halo-5-substituted-pyridines which include reacting a 1,3-dihalopropene of the formula 
wherein X is halo and R2 and R3 are each H or a lower alkyl or benzyl group, with acrylonitrile so as to form a cyclizable intermediate. The intermediate is then cyclized to form a 2-halo-5-substituted-pyridine of the formula: 
wherein X, R2 and R3 are as defined above, and W is H or halo. In particular, where the cyclization is conducted in the presence of a halogenating agent, W will be halo. Where the cyclization is conducted in the absence of a halogenating agent, W will be H.
Another specific preferred embodiment of the invention provides a process for forming a pyrimidine of the formula 
wherein Z is O, S, or NH, and R2, R3 and R4 are each H or a straight chain lower alkyl or benzyl group, which includes reacting a compound of the formula 
wherein X is halo and R2, R3 and R4 are as defined above, with a compound of the formula H2Nxe2x80x94CZxe2x80x94NH2 wherein Z is as defined above, so as to form a cyclizable intermediate, and then cyclizing the intermediate to form the pyrimidine. As examples, X can be O providing urea as a starting material, which can be used in conjunction with the 1,3-dihalopropene to prepare 2-hydroxy-pyrimidines. In a corresponding synthesis, thiourea (Xxe2x95x90S) cab be used to prepare 2-sulfhydryl-pyrimidines. In still further syntheses, guanidine (Xxe2x95x90NH) can be used to prepare 2-amino-pyrimidines.
In another specific preferred embodiment of the invention, a process is provided for preparing a 2-halo-3-substituted pyridine. In this process, a 1,3-dihalopropene is reacted with a compound of the formula NCxe2x80x94CH2xe2x80x94R5, wherein R5xe2x95x90COOR6, CN, CON(R6)2, or COR6, wherein R6 is H or an alkyl, aryl or aralkyl group having 1 to about 10 carbon atoms, to form a 2-halo-5-R5-pyridine.
In the area of pyrazoles, the invention provides a specific preferred embodiment for the preparation of a pyrazole of the formula 
by reacting a compound of the formula H2Nxe2x80x94NHR7, wherein R7 is H or an alkyl, aryl or aralkyl group having up to about ten carbon atoms, with a compound of the formula 
wherein X is halo and R2, R3 and R4 are each H or a straight chain lower alkyl or benzyl group, to form a cyclizable intermediate, and cyclizing the intermediate to form the pyrazole.
In the field of quinolines, in accordance with a specific preferred embodiment of the invention, quinolines can be prepared by reacting an aniline of the formula 
wherein R8, R9, R10 and R11 are each H or an alkyl, aryl or aralkyl group having up to about ten carbon atoms, with a compound of the formula 
wherein X is halo and R2, R3 and R4 are each H or a straight chain lower alkyl or benzyl group, to form an N-(3-halo-2-propenyl)aniline of the formula 
wherein X, R2, R3, R4, R8, R9, R10 and R11 are as defined above. This aniline can in turn be cyclized to form a quinoline of the formula 
wherein R2, R3, R4, R8, R9, R10 and R11 are as defined above.
In still another specific preferred embodiment, the invention provides a for preparing a 2-halo-3-substituted-pyridine, which includes reacting a 1,3-dihalopropene of the formula 
wherein X is halo and R2, R3 and R4 are each H or a lower alkyl or benzyl group, with a compound of the formula CNxe2x80x94XCxe2x88x92xe2x80x94R5 wherein X is halo, R5 is COOR6, CN, CON(R6)2, or COR6, wherein R6 is H or an alkyl, aryl or aralkyl group having 1 to about 10 carbon atoms, so as to form a cyclizable intermediate; and
cyclizing said intermediate to form a 2-halo-3-substituted-pyridine compound of the formula: 
wherein X, R2, R3, R4 and R5 are as defined above.
The invention thus provides processes for preparing a variety of heterocycles having one or more nitrogen or oxygen heteroatoms utilizing readily-available 1,3-dihalopropenes as starting materials, which are reacted with other available starting materials to form the heterocycles. The preferred reactions can be conducted in standard equipment under relatively mild conditions. In addition, processes of the invention involve starting materials which are relatively easy to transport, store and manipulate.
Additional objects, features and advantages of the invention will be apparent from the following description and appended claims.
For the purpose of promoting an understanding of the principles of the invention, reference will now be made to certain preferred embodiments thereof and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations, further modifications and applications of the principles of the invention as described herein being contemplated as would normally occur to one skilled in the art to which the invention relates.
As indicated above, the present invention provides for the production of heterocyclic compounds including a nitrogen or oxygen heteroatom, utilizing a 1,3-dihalopropene starting material as an effective three-carbon fragment. In processes of the invention, either two or three carbons from the 1,3-dihalopropene starting material are incorporated into the heterocyclic ring. For instance, the 1,3-dihalopropene, a 1,3-electrophile, can be reacted with a 1,3-nucleophile so that three carbons from the 1,3-dihalopropene are incorporated into a heterocyclic ring, e.g. in the synthesis of 2-halo-3-substituted pyridines, pyrazoles, oxazoles, and quinolines as described herein. In other reactions, the 1,3-dihalopropene is reacted with another compound, and the formed intermediate cyclized in the presence of a halogenating agent, wherein two carbons of 1,3-dihalopropene starting material are incorporated into the heterocyclic ring, and the third carbon is advantageously incorporated as a substituent on the ring, for instance in the synthesis of certain 2-halo-5-substituted pyridine compounds as described herein. These reactions, particularly in those cases wherein 3 carbons of the 1,3-dihalopropene are incorporated into the heterocyclic ring, can be conducted in the presence of a catalyst which facilitates the nucleophilic displacement, for example a palladium catalyst such as a ligated palladium zero complex.
Preferred processes of the invention generally include the steps of reacting a 1,3-dihalopropene compound of the formula 
wherein X is halo such as chloro, bromo or iodo, R1 is H or R4 wherein R4 is H or a straight chain lower alkyl or benzyl group, and R2 and R3 are each H or a straight chain lower alkyl or benzyl group, with a second reactant, optionally in the presence of a catalyst as discussed above, to form an intermediate cyclizable to form the desired heterocyclic compound. The intermediate is then cyclized to form the desired heterocyclic compound. In these regards, this 1,3-dihalopropene starting material can be a cis- or trans-isomer, or a mixture of such isomers, and any intermediates formed can likewise have cis- or trans-configurations, or a mixture thereof.
Each of the reactions involved in the syntheses described herein can be conducted for any suitable time to yield the desired product, typically up to about 20 hours, more preferably up to about 10 hours. The halogenating agent, when used, can include any suitable source of halogen, including for example molecular halogen and compounds which dehalogenate under the reaction conditions, e.g. a sulfuryl halide which dehalogenates to produce molecular halogen. Preferred halogenating agents include those which provide molecular chlorine, molecular bromine and/or molecular iodine, most preferably molecular chlorine. In one preferred form, gaseous chlorine can be fed to and reacted with a liquid reaction mixture to form the desired compound.
Reactions in accordance with the invention are preferably conducted in an organic solvent, although they also may be conducted neat. Preferred solvents are aprotic solvents, with illustrative solvents including cyclic or acyclic ethers, including dioxanes, cyanoalkanes, e.g. acetonitrile and proprionitrile, ethyl acetate, and the like.
As disclosed above, 1,3-dihalopropenes (optionally further substituted with hydrocarbon groups) provide effective reactants in the synthesis of a variety of heterocyclic compounds containing one or more nitrogen and/or oxygen heteroatoms. In particular, Table 1 and Schemes 1-7 below illustrate preferred syntheses of the present invention. Specifically, Table 1 shows preferred Additional Reactants (other than the 1,3-dihalopropene also included), preferred Solvents, and preferred Reaction Temperatures which can be used, and the preferred Products classes which are formed. Schemes 1-7 show expected intermediates and final products resulting from the reaction of the Additional Reactants shown in Table 1 with a 1,3-dihalopropene. In Schemes 1-7, R2, R3, and R4 are generally H, straight chain lower alkyl (C1 to C6 alkyl) groups, or benzyl groups; R8-R11 are each H or an alkyl, aryl or aralkyl group having up to about ten carbon atoms; and the remainder of the variables are as defined in Table 1. In addition, the usage is the Schemes and elsewhere herein of the wave-line  denotes a carbon bond in which no particular stereochemistry is intended (i.e. the compound can be cis-, trans- or a mixture of cis- and trans-isomers), and the usage of the symbol [O] denotes oxidative conditions, for example as can be achieved in the presence of a suitable oxidizing agent such as a peroxide, e.g. hydrogen peroxide, nitric acid, manganese dioxide, permanganate, a chromium compound, and/or an oxygen-rich environment. These and other expedients, for example the use of appropriate catalysts for the reactions as described herein, will be within the purview of those skilled in the area.

The heterocycle products of the invention are generally useful as active agents or as intermediates to active agents employed in pesticidal, herbicidal and/or medicinal compositions. As specific examples, 2-chloro-3-substituted pyridines such as 2-chloronicotinic acid are used as intermediates to a variety of agrochemicals, including herbicides, as well as medicinal compounds such as enzyme inhibitors.
For the purposes of promoting a further understanding and appreciation of the invention and its various advantages, the following specific Examples are given. It will be understood, however, that these Examples are illustrative, and not limiting, in nature.